In recent years methods and cameras have been proposed for combining IR images and visible light images in various ways, often referred to as image fusion. Typically, a camera will have an imaging part for capturing IR image data, another imaging part for capturing visible light image data and means for processing the image data in such a way that they can be displayed in the same image. Such functions may be helpful, for example, in identifying the position of a hot, or cold, object.
Typically, the field of view of the visible light image is greater than the field of view of the IR image. In any case the fields of view will differ, since the optical systems capturing the two images will not be placed in exactly the same position. This is a well known optical phenomenon called parallax. Hence, before displaying a fused, or blended, image the two images must be aligned.
EP patent 1 299 699 discloses a method of displaying visible light image data and IR image data in the same image, and a camera comprising imaging means both for IR radiation and visible light. The data can be combined in a number of different ways, for example, in dependence of the temperature of each respective pixel.
This patent also mentions the need for correcting the parallax caused by the image capturing means for IR and visible light, respectively, being placed at a certain distance from each other. Two main methods of parallax correction are suggested: by optical means such as mirrors or by electronic means. How to correct the parallax by electronic means is not discussed in detail.
International patent application WO 2006/060746 discloses parallax correction based on the distance to the object. The distance to the object is in turn determined by the focusing distance. The method suggested in WO 2006/060746 is to use a magnet mounted on the IR lens and a Hall sensor mounted in the optics housing, or vice versa, whereby the Hall sensor will measure the distance to the magnet and hence the focusing distance. The actual focusing of the camera is performed manually, in a way known per se, by turning a focus ring. As an alternative it is suggested to align the images by manually displacing one relative the other until they overlap correctly.
A number of ways of combining the IR and visible light image data are proposed in WO 2006/060746. For example, the visible image may be shown in a grey scale and the IR image superimposed on this image in colour. Alternatively, the visible light image may be displayed, but for pixels in which the temperature values exceed a certain threshold value the visible light pixels may be replaced by IR image pixels.
It is an object of the present invention to improve the presentation of the combined IR and visible light image.